ironically the glasgow accent is one of the easier to understand, easy to pick due to how much they stretch the vowels. Mind you my whole family is from scotland. There are some parts of scotland (I think somewhere around dundee or maybe the firth of forth but could be off a good distance) where the accent is so thick even people from Endinburgh and to a lesser extent Glasgow can struggle to understand them. If you want a real head trip visit the outer hebrides. The accent is softer (to my ears since it's closer to my relatives) but most of the people out there are still fluent in scottish gaelic whic sounds odd to English speakers to say the least. It's on my bucket list to head out there.